**Contact Info**

Department of Applied Mathematics

University of Waterloo

Waterloo, Ontario

Canada N2L 3G1

Phone: 519-888-4567, ext. 32700

Fax: 519-746-4319

PDF files require Adobe Acrobat Reader

Wednesday, May 7, 2014 9:30 AM EDT

MC 6496

Sepideh Afshar, Department of Applied Mathematics, University of Waterloo

Lithium-Ion battery SOC estimation

In recent years, electric and hybrid vehicles (EV/EHV) are becoming more attractive because of higher fuel efficiency and lower emissions. Batteries are the storage unit of electric vehicles and cells are their elementary units. Tracking the state-of-charge (SOC) of each cell in a battery pack is a key requirement for calculating the vehicle's range and driver's peace of mind. Although direct and precise measurement of SOC of a cell is not achievable by existing sensors, other quantities like battery terminal voltage and current can be easily measured. At every measurement step, the cells SOC is determined and updated via the available measurements.

The importance of accurate estimation of SOC is even more crucial in HEVs comparing to EVs since their environment characteristics are more demanding. Therefore, an appropriate method of more accurate estimation of SOC from available measurements are needed. In general, electrochemical model-based estimation methods provide higher accuracy; however, simplifying the governing equations is required to their complexity. So far, the simplified models in the literature lack the accuracy in estimatining SOC for chemical compositions like Lithium ion phosphate, LiFePO4, (LFP) at high current rates. The main weakness of these models is the poor approximation of cell's hysteretic behavior, a critical phenomenon in LFP cell's response.

As the first step of designing an observer, the electrochemical model must be studied for its important features including the nonlinearities, the properties of equilibrium points, and observability. The simplified model must preserve the affecting portion of the dynamics, the location and properties of the equilibrium points and the observability of the state vector. In this report, the electrochemical governing equations are first simulated in COMSOL to investigate the existence of hysteresis in system response. After finding the equilibrium solutions of the system, a simplified model based on linearizing the system around some equilibrium points is developed. Next, sliding mode observer is introduced as a robust observer for SOC estimation.

Location

MC - Mathematics & Computer Building

MC 6496

200 University Avenue West

Waterloo, ON N2L 3G1

Canada

200 University Avenue West

Waterloo, ON N2L 3G1

Canada

**Contact Info**

Department of Applied Mathematics

University of Waterloo

Waterloo, Ontario

Canada N2L 3G1

Phone: 519-888-4567, ext. 32700

Fax: 519-746-4319

PDF files require Adobe Acrobat Reader

University of Waterloo

University of Waterloo

43.471468

-80.544205

200 University Avenue West

Waterloo,
ON,
Canada
N2L 3G1

The University of Waterloo acknowledges that much of our work takes place on the traditional territory of the Neutral, Anishinaabeg and Haudenosaunee peoples. Our main campus is situated on the Haldimand Tract, the land granted to the Six Nations that includes six miles on each side of the Grand River. Our active work toward reconciliation takes place across our campuses through research, learning, teaching, and community building, and is co-ordinated within the Office of Indigenous Relations.